How do they even know if someone is carrying alcohol?
I say it's a free country, ...and they have the right to refuse carriage to anyone carrying alcohol, or travelling with a seeing eye dog if that's what they believe. By exercising that right, ...they also have the right to seek employment in some other capacity. By the same token, the cab companies also have the right as well as duty to fire their asses, ...and the city or whoever licenses cabs has the right to revoke and/or refuse to re-issue their licenses for discrimination. Their beliefs are one thing, ...however, when it infringes upon the lawful rights of others... they have no business being in a capacity that demands the rights of others be trampelled so they can practice their beliefs. Time for those cabbis to get a different job.
Probably people carry alcohol separately, in duty-free bags?
Or if they're like me... you can hear their clanging bottles in the suitcase a mile away.
Immigrants are often taxi drivers, and Sommalians tend to be strict about interpreting their religion so makes sense the dispute would center around this particular business. But, what you say is true... there are other means of gainful employment that wouldn't infringe on their beliefs.